Something Fishy

Screen shot 2013-03-15 at 8.07.42 AMIt’s Lent. It’s Friday. And the world is a buzz over Pope Francis I. It’s seems like a great time to share a few thoughts about fish allergies which are one of the most common food allergies in adults.

Can someone allergic to shrimp eat lobster? (No.) What about oysters? (Probably.) Could they still eat salmon or sea bass? (Yes.)

As with all food allergies, it is best to see a board-certified allergist to review the history, undergo testing to confirm the sensitivity and determine the best treatment to minimize future risk. This usually entails avoiding the causative food and carrying injectable epinephrine to use for life-threatening reactions.

Most patients will present with a reaction to shellfish or fish. Shellfish can be further broken down into categories of crustaceans (shrimp, lobster, crab, crawfish) and mollusks (oysters, mussels, scallops). Shellfish allergies are estimated to affect over 2% of the U.S. population. The major allergen in shellfish is a substance called tropomyosin. It tends to be present in all crustacea and can even have some cross-reactivity to dust mites and cockroaches. I point out to patients that this group includes all organisms with a shell including shrimp, lobster, crab and crayfish. Meaning, if you are allergic to shrimp, it’s very likely other organisms with a “shell” will cause similar problems. Cross-reactivity to mollusks or bivalves and shellfish is less defined. An allergist can confirm a lack of reactivity to oysters even if someone is allergic to shrimp for instance. Shellfish and vertebrate fish do not cross-react. Assuming there was no cross-contamination in the preparation of the food, someone allergic to shrimp can still eat sea bass. (That’s a relief because sea bass is so good!)

The major allergen in finned fish, like cod, is a substance called parvalbumin. Over ten common fish species have a similar protein which means there can be significant cross-reactivity in this group as well. It seems to be less defined and skin testing can help identify types that might be okay to try under the supervision of an allergist.

It is a common misperception that seafood allergy is associated with reactions to radiological contrast dye. The reactions have different causes and are not associated.

Unfortunately, the natural history of fish and shellfish allergies is similar to peanut. Once allergic, it is less likely to be “outgrown” compared to egg or milk.

Be sure to “like” my facebook page at www.facebook.com/drdamin, follow me on Twitter and share this page with other allergy sufferers.

Disclaimer: This blog is not intended to create a doctor-patient relationship with any reader. If you need personalized medical advice, contact your primary care physician or other physician in your community.

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